The present invention relates to a hydraulic self-adjusting device for clutch control cables which, in particular, is applicable as a compensating device for the clutch plate lining wear in motor vehicles.
It is known that operation of a motor vehicle clutch causes continuous wear of the clutch plate lining, involving the need to adjust the pedal travel periodically to maintain it constant and in this way compensate for the said wear. Since these adjusting operations are, in general, costly, there are available self-adjusting devices, installed as original equipment in motor vehicles, which compensate for the clutch plate lining wear by the corresponding variation of the length of the control cable linking the clutch mechanism with the control pedal therefor.
Among the known embodiments of the above mentioned self-adjusting devices, the hydrauliuc devices allow for continuous adjustment of the control cable length without any discontinuity occurring therein, unlike the self-adjusting devices based on the coupling of mutually telescopically sliding members using mechanical toothing for setting the cable length.
The hydraulic self-adjusting devices are attached to the clutch mechanism pressure plate operating fork and compensate for the clutch plate lining wear by increasing, to a corresponding extent, the length of the control cable connecting the self-adjusting device to the clutch pedal, without there being any discontinuity caused in the said control cable, as said above.
Generally speaking, the known hydraulic self-adjusting devices for clutch control cables comprise all or some of the following operating members:
a body member provided with means for attachment thereof to the clutch mechanism pressure plate operating fork and containing a piston fixedly attached to an adjusting rod which is connected at one end thereof to the corresponding end of the control cable extending to the clutch pedal; PA1 a piston with through holes allowing the liquid contained in the device body member to flow therethrough; PA1 and a control spring which permanently bears at one end thereof against the self-adjusting device and which bears at the other end thereof against the corresponding end of the said adjusting rod so as to pull permanently against the control cable. PA1 a hollow generally cylindrical elongate main housing having at the two ends, respectively an open front port provided with an end cap and a closed rear extension allowing it to be connected to the clutch mechanism pressure plate operating fork, said main housing containing a liquid; PA1 a piston contained in the main housing and capable of adjustably sliding along a portion delimited by two terminal stop positions and which allows the fluid contained in the main housing to flow therethrough through a pertinent passage; PA1 an adjusting rod, having one end thereof passing through the closed rear extension of the main housing and attached to the corresponding end of the control cable connecting with the clutch mechanism operating pedal; PA1 and a control spring permanently urging the adjusting rod so that the clutch mechanism control cable is pulled; PA1 the adjusting rod extends to the outside only at the rear end of the main housing, the other end of said rod remaining permanently in the main housing fixedly attached to the piston; PA1 the passage in the piston for fluid flow therethrough is provided with a shut-off valve formed by a passage member fixedly attached to the adjusting rod and by a shut-off member which may cut off the fluid flow through the passage member depending on the movements of the adjusting rod, and said shut-off member may be complemented operatively with an opening spring; PA1 and the control spring is contained in the main housing coaxially with the adjusting rod, with one end bearing against the bottom of the inside rear end of said housing so that the other end permanently urges the adjusting rod either directly or by bearing first against the piston attached to the rod. PA1 the passage member is essentially cylindrical and is attached to the adjusting rod by means of an axial hole provided with a screw thread and is formed, laterally, with a concentric groove housing a sealing gasket and, at the end facing the adjusting rod, with a smaller diameter cylindrical extension, said passage member having a sufficient number of longitudinal through holes equidistant from the centre line thereof and centered around the base of said extension; PA1 the shut-off member is essentially cylindrical and is disposed coaxially around the adjusting rod on which it may slide and is formed, laterally, with a perimetral flange and, at the end facing the passage member, with a coaxial groove snugly housing a sealing gasket which may seal the through holes of the passage member; PA1 and the opening spring is disposed coaxially around the adjusting rod between the passage and shut-off members so that one of the ends thereof bears against the passage member on the step defined by the cylindrical extension with which it is formed and the other end thereof bears against the perimetral flange of the shut-off member. PA1 the passage member is formed by a base member and by a guide member, both essentially cylindrical and mutually engageable by way of corresponding screw threads, the guide member being attached to the adjusting rod by way of an axial hole provided with a screw thread; PA1 the base member is formed, laterally, with a concentric groove housing a sealing gasket and, longitudinally, with a through hole defining four cylindrical portions of decreasing diameter, the first largest diameter portion being provided with a screw thread and housing the guide member, the second and third portions containing the shut-off member and the opening spring, respectively, and the fourth portion is the fluid passage portion, with the entry to the third portion forming a closing seat; PA1 the guide member is formed, laterally, with a screw thread and, longitudinally, with a sufficient number of through holes establishing communication between the main housing chamber adjacent thereto and the second portion of the base member through hole and, at the end facing the base member with an axial hole partly housing the shut-off member; PA1 the shut-off member has a surface of revolution, is essentially cylindrical and is formed at the end facing the base member with a profile functionally mating with the closing seat formed on the entry to the third portion; PA1 and the opening spring constantly presses against the bottom of the third portion and the corresponding end of the shut-off member. PA1 the passage member is essentially cylindrical and is attached to the adjusting rod by means of an axial hole provided with a screw thread and is formed, laterally, with a concentric groove housing a sealing gasket and longitudinally, with a sufficient number of through holes for guiding the shut-off member and one or more through holes each formed by two cylindrical portions of different diameter joined by a frustoconical portion forming a closing seat; PA1 the shut-off member is essentially cylindrical and is disposed coaxially around the adjusting rod on which it may slide and is formed, on the side facing the passage member, with guide pins in the same number as the through holes provided for that purpose in the passage member and a closing pin for each through hole, the free end of which is conical mating with the respective closing seat formed on the passage member; PA1 and the opening spring is disposed, like the shut-off member, coaxially around the adjusting rod so that the ends thereof bear permanently against the passage and shut-off members, respectively. PA1 the passage member is essentially cylindrical and is attached to the adjusting rod by means of an axial hole provided with a screw thread and is formed, laterally, with a concentric groove containinga sealing gasket and, at the end facing the adjusting rod, with a frustoconical inlet hole forming a closing seat, the passage member having a sufficient number of longitudinal through holes extending between the bottom of the frustoconical inlet hole and the opposite end of the passage member; PA1 the shut-off member is essentially cylindrical and is disposed coaxially around the adjusting rod on which it may slide and is formed, laterally, with a frustoconical surface mating with the closing seat formed on the passage member and, on the side facing said passage member with an axial cylindrical flange; PA1 and the opening spring is disposed coaxially around the adjusting rod between the passage and shut-off members so that one of the ends thereof bears permanently against the bottom of the frustoconical inlet hole of the passage member and the other end against the step defined by the axial cylindrical flange of the shut-off member. PA1 the passage member is essentially cylindrical and is attached to the adjusting rod by means of an axial hole provided with a screw thread and is formed, laterally, with a sufficient number of longitudinal grooves; PA1 and the shut-off member, which is attached to the passage member and is disposed coaxially around the adjusting rod, is essentially cylindrical and is formed, at the end facing the passage member with a cylindrical portion of smaller diameter which may snugly house and retain a resilient material sealing gasket which may, by resilient deformation, press against the inner wall of the main housing, preventing liquid flow between the chambers.
British patent 2,018,933 for "Hydraulically damped automatic play compensation device for motor vehicle clutches" may be cited as an example of known self-adjusting hydraulic devices for control cable lengths. This comprises all the operating members succinctly described above, apart from its own unique characteristic members.
Generally speaking, the known embodiments of self-adjusting hydraulic devices have a large number of components of complex manufacture and assembly, notably increasing the cost of the finished product. For their very complexity and the working conditions to which they are subject, they cause frequent faults and/or misoperation.